Blinds having a head rail and blind slats suspended from the head rail are well known. Such blinds include “venetian” blinds in which the slats run from side to side, horizontally, and also vertical blinds in which the slats hang vertically down from trollies carried in the head rail.
For many years such head rails have been made of metal. Usually they have been formed in the shape of a rectangular U-shaped channel, with the blind operating and control mechanism located in the channel.
In recent years however customers have been seeking a more economical form of blind. Head rails for less expensive blinds are now commonly made of extruded plastics material, such as polyvinyl chloride materials. Such materials have their advantages such as low cost and freedom from maintenance and the like. However customers are always seeking for new and different visual effects in blinds. In one case it has become the practice to make the blind slats themselves of extruded plastic materials. These are both less expensive than metal blind slats, and also provide a more solid look than conventional thin metallic blind slats.
However the use of such thicker plastic blind slats carries with it the penalty of greater weight. In fact for a given size of window the use of thicker plastic slats, can increase the weight to the point where they will impose bending stresses on the extruded plastic head rail, and it will bow downwardly in the centre.
This is both unsightly, and may also cause malfunction of the blind control mechanism located within the head rail.
The problem could be overcome by using a conventional metallic head rail, but this would increase the cost, and might also affect the appearance of the blind.
Another factor in the marketing of such blinds is that is becoming the custom to market these blinds through department stores. Blinds are supplied to the store in standard widths. A customer will measure the actual window or door opening in which he wishes to erect a blind. He will then place his order in the store. The sales clerk will then select a blind having a width greater than that required by the customer.
He will then trim the ends of the blind head rail and the blind slats (and the bottom rail if provided) so as to fit the customer's requirement.
Various machines are available for trimming blinds. Some use cutting blades. Others use actual profiled cutting dies, especially for cutting metallic head rails.
Examples of such in store point of sale blind trimming machines can be seen in U.S. Pat. Nos. 5,806,394; 6,196,099; 6,178,857; 6,089,134; all of which are owned by Shade-O-Matic Llimited, also the owner of the present application.
However, where the blinds have a plastic head rail, and extruded plastic slats, and a bottom rail in some cases, it is preferable to cut them with a saw. The plastic is softer and at the same time thicker than the metal used for conventional head rails. Thus in the case of a blind having a plastic head rail, and plastic blind slats, the length of the cutting stroke required to cut a given number of plastic blind slats is increased compared with cutting the same number of metal blind slats. Cutting such plastic slats with a knife edge requires considerable effort. It also tends to damage the plastic at the ends of the slats. Because the stroke required to cut the stack of thicker plastic blind slats is much longer than the stroke required to cut thin metal blinds slats, then either the manual effort required to make the cut must increase, or the leverage available in the cutting machine must be increased. Neither is desirable or practical. It is in fact found that the use of a saw, typically a rotary saw disc will provide a quick clean cut through the relatively softer plastic blind slats, and also the plastic head rail, with a minimum of physical effort.
This also has the added advantage that the head rail, usually a U-shaped channel, can be cut cleanly with a saw, without the need for supporting it in a special die. Such rotary saw cut down equipment is now becoming widely available in retail stores, rendering it possible to such stores to meet public demand for low cost blinds, trimmed to size on demand, in the store.
However, if the plastic head rail is not capable of supporting the weight of the blind slats then it should preferably be given some kind of reinforcement such that it will be effective to prevent sagging under the weight of the plastic blind slats.
However, the reinforcement must be such that it does not prevent the head rail from being cut down or trimmed in the in store trimming apparatus, of which the saw cutting equipment now available is one example, in the retail stores.